Computer simulations of a tumor surface octapeptide epitope

Area of Science:

• Computational chemistry
• Molecular modeling
• Biophysics

Background:

• The study focuses on an octapeptide, the N-terminal epitope of an 11 KD glycoprotein antigen found on human ductal carcinoma (breast) cells.
• This octapeptide is poorly soluble, posing challenges for structural analysis.

Purpose of the Study:

• To explore the conformational landscape of the octapeptide using molecular dynamics simulations.
• To identify the lowest potential energy conformation of the octapeptide.

Main Methods:

• Utilized molecular dynamics simulations with CHARMM and GEMM programs on a Star Technologies ST 100 array processor.
• Performed simulations at both 600 K and 300 K, employing alpha-helix and N-acetyl-N1-methylamide derived starting structures.
• Required very long simulations, on the order of nanoseconds.

Main Results:

• Identified a stable lowest potential energy conformation for the octapeptide.
• This conformation was consistently found from both starting structures at 600 K.
• At 300 K, the same conformation was only achieved using the N-acetyl-N1-methylamide derived starting structure.
• The lowest energy conformation is characterized by 4 hydrophobic contacts and 13 hydrogen bonds, forming one turn of a left-handed helix.

Conclusions:

• The N-acetyl-N1-methylamide derived structure is a reliable starting point for conformational exploration at physiological temperatures.
• The identified left-handed helical conformation is stabilized by specific hydrophobic and hydrogen bonding interactions.
• This conformational insight is vital for understanding the structure and potential function of the breast cancer-associated glycoprotein antigen.